Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of emissions. The emissions may include both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles generally referred to as soot.
Environmental concerns have resulted in the development of systems to treat engine exhaust. Some of these systems may employ exhaust treatment devices, such as particulate filters, to remove particulate matter from the exhaust flow. A particulate filter may include filter material designed to capture particulate matter. After an extended period of use, however, the filter material may become partially saturated with particulate matter, such as soot. This partial saturation may hinder the ability of the particulate filter to remove particulates from the exhaust flow.
A large portion of the collected particulate matter, e.g. soot, may be removed from the filter material through a process called regeneration. One way that regeneration may be accomplished is by increasing the temperature of the filter material, and the particulate matter in the filter material, above the combustion temperature of the particulate matter. The soot may be consumed by the heat of the regeneration process. However, a portion of the particulate matter, e.g. ash, may remain in the filter material and, over time, accumulate. As ash accumulates, the efficiency of the particulate filter to control emissions of particulate matter may be adversely affected.
Ash derives largely from engine lubricating oil that, unavoidably, finds its way into the engine combustion chambers, and is consumed during the combustion phase of engine operation. Different engine oil formulations contain varying amounts of ash. An engine that is lubricated by an oil formulation with a higher ash content will, all other factors being equal, place more ash into the engine exhaust system, and thus, into aftertreatment elements, such as, for example, a particulate filter. In addition, engine system failures, e.g. deteriorating piston rings, may result in higher than normal oil consumption and, hence, higher ash accumulation rates in an aftertreatment element.
It is desirable that there be some effective manner for compensating for variability in ash accumulation rates, and otherwise maintain particulate filter efficiency, by accounting for ash accumulation.
One regeneration system that accounts for ash accumulation is disclosed in U.S. Pat. No. 5,195,316, issued to Shinzawa et al. on Mar. 23, 1993 (“the '316 patent”). The '316 patent discloses embodiments that advance the timing of initiation of regeneration in accordance with the accumulated amount of incombustible residue in a particulate trap. The '316 patent discloses that it is possible to sample pressure differentials after regeneration and then determine the amount of accumulated incombustible residue. The frequency of regeneration can then be increased as the amount of incombustible residue increases in order to allow for the fact that the trap will tend to reach a fully charged state earlier than normal due to the incombustible residue that has accumulated.
While the system of the '316 patent contemplates varying regeneration frequency as ash accumulates, no provision is made for a correlation between tracked minimum flow resistance values through the particulate trap over time, with a model of engine oil consumption rate that is based on predetermined values for engine oil consumption. In addition, the system of the '316 patent does not contemplate adjusting the predetermined values of the model for engine oil consumption rate based on the tracked minimum flow resistance values. Accordingly, the system of the '316 patent may not properly take into account the impact of a major contributor to ash accumulation in a particulate trap. Not directly accounting for the impact of consumed engine oil, may result in inaccurate determination of remaining particulate trap volume, improperly timed servicing of the particulate trap for ash removal, and adverse effects on fuel consumption when ash accumulation has been underestimated.
The disclosed methods and systems for maintaining particulate filter efficiency are directed toward overcoming one or more of the problems set forth above.